five nines
jargonops cultureISP & telecom
99.999% availability - about five minutes of downtime allowed per year.
The classic telecom gold standard. Each added nine costs roughly ten times more than the last: four nines is under an hour of downtime a year, five is minutes, six is seconds. The honest question is never whether you can hit five nines, but which failures the users actually feel.
Also known as: 99.999%, five 9s